Electrical gaseous discharge device



April 16, 1940. c, s rr 2,197,398

ELECTRICAL GASEOUS DISCHARGE DEVICE I Filed Nov. 4, 1936 2 Sheets-Sheet1 N I T 1 bi *1 A m I 63 $2. uanunn I11 veflzfor CHARLES 6. SM/TH bywrit $232??? 1940- 7 Q 0. 6. SMITH 7,3 8

ELECTRICAL GASEbUS DISCHARGE DEVICE Filed Nov. 4, 1936 2 Sheets-Sheet 2Iwvenfar CHARLES G 5mm Patented Apr. 16, 1940 ELECTRICAL GASEOUSDISCHARGE DEVICE Charles G. Smith, Medlord, Mara, assignor to RaytlieonManufacturing Company, Newton, Mass., a corporation of DelawareApplication November 4, 1936. sci-n1 No. 109,137

18 Claims.

This invention relates to an electrical gaseous discharge device, andmore particularly to such a device which is adapted to operate as arectifier.

An object oi. this invention is to produce such a device which has anabnormally low voltage drop during the conducting phase during whichlarge currents can be carried.

Another object is to produce such a device which can withstand high orlow reverse voltage without any substantial chance of flashback.

A still further object is to produce such a device in which theconduction of current can be controlled in both the forward and in threverse direction.

The foregoing and other objects of my invention will be best understoodfrom the following description of exemplifications thereof, referencebeing had to the accompanying drawings, wherein:

Fig. 1 is a diagrammatic view showing a. tube in. section constitutingone embodiment of my invention, together with an associated circuit withwhich it may be used;

Fig. 2 is a diagrammatic view showing a tube in section constitutinganother embodiment of my invention; and

Fig. 3 is a diagrammatic view showing a tube in section constitutinganother embodiment of my invention in which the conduction of currentcan be more easily controlled.

The present invention is based upon certain observaticns of mine dealingwith mercury vapor in the pressure region of the order of .001 mm. ofmercury and lower. I have discovered that a ring or electrodelessdischarge of considerable current (measured in some cases in hundreds ofamperes) can be passed through mercury vapor with small voltage drop (5volts more or less) when the vapor pressure is in the region mentioned.The requirements for passing such current are a region of considerablevolume and a few electrons for initiating the discharge to make a supplyof ions for a current between a filament and a cool anode. The supply ofions near the cathode needs, in some cases, to be only enough toneutralize the electronic space charge. Near the anode enough ionizationshould be produced to give a random electronic current shower upon theanode equal to the current carried by the rectifier. For this reason andfor purposes of heat radiation, the anode is of considerable area and ispreferably placed in a region of great ionization.

Before describing the construction shown, a

few remarks concerning the nature of the discharge used are in order.

It is. commonly observed that space current between a thermionic cathodeand an anode in a mercury vapor device will pass readily at a pressureof say .01 mm. in ordinary cases, which may be termed a relaxed gaseousdischarge". Ii the pressure is reduced, 8. point is reached where thecurrent begins to be limited. This may occur at a pressure'as high as.001 mm. in some cases.

When the pressure is decreased to zero, the voltage drop for conductionis that required by space charge limitations, and the practical currentis measured usually in milliamperes. While the present tube is notlimited to operation in this transition pressure region between a highvacuumand a relaxed gaseous device, it is adapted for such operation.

The device shown in Fig. 1 comprises a sealed envelope l of somesuitable material, such as glass, containing a cylindrical anode 2having open ends, whereby current carriers can pass from one side of theanode to the other. This anode is of considerable area as specifiedabove. The envelope also contains a thermionic cathode 3 which issupported on a stem 4. A small auxiliary anode 5 may also be supportedon the stem 4. The auxiliary anode 5 is used mainly for startingpurposes. The gas pressure is low and preferably of the order specifiedabove. In each case, however, the gas pressure is so related to thespacing between the cathode and anode and the rest of the geometry ofthe device that in absence of any outside supply of ions, a high voltagedrop would exist between the cathode 3 and anode 2 which would tend toprevent any appreciable passage of current between them. Thus a separate'source of ions, as described below, is used.

The envelope l is provided with a bulbous enlargement 6 in which a ringdischarge of the type described above may-be produced. In order toproduce such a discharge, a, coil 1 surrounds the enlargement 6. Thecoil 1 is energized from some suitable source of high frequency currentwhich may be an oscillator 8'supplied with power through conductors 9and l0 from a suitable source of alternating current. The anode 2 ispreferably slotted in order to prevent the inducing of a large highfrequency current therein.

- In order to maintain the desired low pressure, the envelope I isprovided with a tubularextension ll projecting away from the envelope Iand inwhich the vapor filling of the tube may condense. Such vapor maybe, for example, mereury vapor supplied from a drop 01' mercury IIplaced in the extension H. The pressure in the envelope I may becontrolled by controlling the temperature of the extension II which maybe artificially cooled if desired. It is to be understood that othervapors or gases at the desired low pressures may be utilized. Thepressure, as indicated above, should be low and preferably of the orderof .001 mm. of mercury or lower. 7

The cathode 3 may be heated from a heating transformer l3 whosesecondary I4 is connected to the terminals of the cathode and whoseprimary i5 is connected to a source of alternating current. The currentto be rectified may be derived from an input transformer l5 whoseprimary winding I1 is connected to a source of alternating current. Oneend of the secondary ll of the transformer It has connected thereto aconductor I9 which extends to one terminal of a load device whose otherterminal is connected to the anode 2. The other end of the secondary I6is connected by a conductor 2! to an inter-' mediate point on thesecondary winding l4.

A discharge may be maintained between the cathode 3 and the auxiliaryanode 5 by having a conductor 22 extend from the conductor l3 andthrough a current-limiting resistor 23 to the auxiliary anode 5. In thisway the secondary l3 impresses a potential between the cathode 3 and theauxiliary anode 5, and a few electrons flow between these electrodes toproduce a few ions between them.

When the device is connected and energized as described above, inaddition to the discharge between the cathode 3 and the auxiliary anode5, a small current of electrons flows from the cathode 3 to the anode 2,also producing some ions. Some of the ions created by these dischargeswander into the enlargement 8 and initiate an electrodeless dischargeunder the action of the field of the coil 1. The current carriers inthis discharge are caused to travel in circular paths of considerablelength, and considerable amperage flows .in such a discharge. Thisintense discharge creates large numbers of positive ions and electrons,many of which travel down into the region of the anode 2 and the cathode3. Thereupon large currents can be drawn between 2 and 3 at voltagedrops which in many cases may even approach zero or less. Since thevoltage is so low, it is to be noted that the gas pressure is highenough, under the conditions described, to completely neutralize spacecharge, and the discharge can properly be termed arc-like.

. The high frequency source 8 may be modulated by the potential suppliedfrom the conductors 9 and I0 so that a high frequency current isdelivered to the coil I only during the conducting half of the voltagecycle between the cathode 3 and the anode 2. In absence of the ionizingaction of the high frequency coil, it is extremely difiicult to causeany conduction of current through the discharge space. Thus, at the lowpressures specified and particularly under the conditions specifiedabove, the practical voltage that can be rectified is extremelyhigh,.and in some cases may approach those voltages which can berectified by a high vacuum device. For example, voltages of the order ofa thousand volts or more can be rectified.

Instead of an electrodeless discharge, large circulating currents may beproduced in the enlargement 6 in other ways as, for example, by athermionic cathode and an anode, the circulation of current beingproduced by a constant magnetic field at right angles tween theelectrodes.

The supply of positive ions and electrons may be created by a discharge,located in theregion between the main cathode and anode, as shown, forexample, in Fig. 2. In this figure is shown a tube comprising a sealedenvelope 24 containing a cathode 25 and an auxiliary anode 26 supportedon a stem 21, and analogous to the cathode 3, an auxiliary anode 5of'Fig'. 1. A main anode 23 is located at the opposite end of theenvelope from the cathode 25. The anode 23 should preferably extendsubstantially across the envelope 24in order to have the desired area.The envelope 24 has a relatively large cross-sectional area so thatunder the pressure conditions specified, large circulating currents canbe produced therein. For this purpose a coil 23 surrounds the envelope24 in the regionbetween the cathode 25 and the anode 28. This coil 29may be energized as is coil I of Fig. 1. The envelope 24 is alsoprovided with a tubular extension 30 containing a source of vapor, suchas a mercury drop 3|. The device of Fig. 2. when operated under theconditions and in the manner as indicated for Fig. 1, producessubstantially the same type of operation and results assdescribed inconnection with Fig. 1.

The facility with which the high frequency field may control theconduction of current can beincreased by such an arrangement as is shownin Fig. 3. In this figure is shown a tube comprising a sealed envelope32 containing a thermionic cathode 33 which may be of theindirectlyheated type having an interior heater 34. Adjacent the cathode33 is supported an auxiliary anode 35. The cathode 33, the heater 34,and the anode 35 may be conveniently supported on a stem 36 throughwhich lead-in wires for the respective elements are sealed. The cathode33 is placed in a relatively large bulbous portion 31 which issurrounded by a high frequency coil 38, whereupon the ionizingcirculating discharge referred to above may be produced. The pressureconditions within the tube are those also as specified above.

The bulbous portion 31 is provided with a restricted side arm 33 at theouter end of which is supported an anode 40. The anode is supplied witha lead-in conductor 4| sealed through the end of the side arm 39. Theouter end of the side arm may be provided with an appendix 42 in which adrop of mercury 43 may be placed. The temperature of the appendix 42 maybe controlled in any suitable manner to produce the desired low vaporpressure within the envelope 32. The diameter of the side arm 33 is sorestricted that a self-sustaining discharge cannot be maintained to theanode without some additional supply of ions other than the dischargebetween the cathode 33 and the anode 40. restriction of the side arm 33produces a greater loss of ions on the walls of said side arm so thatthe discharge itself between the cathode 33 and the anode 40 does notcreate a suflicient number of ions within the side arm- 39 to compensatefor the rate at which these ions are lost. However, the ionizingcirculating discharge which is produced by the high frequency coil 38within the bulbous portion 3'! creates a large number of ions which areshowered down upon the open end of the side arm 39, and at the lowpressure specified penetrate into the' side arm in sufficiently greatnumbers so that the loss of ions on the side walls of said side arm iscompento the path be- Themenace sated for and relatively greatdischarges at low voltages may easily be maintained under theseconditions. Of course it is to be understood that instead of providing aside arm, such as 39, other utilized.

When the cathode 33 is heated to temperature of thermionic emission bythe heater 34, a small discharge will flow to the auxiliary anode 35,creating a few ions which enable the high frequency coil 38 to set upthe intensely ionizing circulating discharge within the bulbous portion31'. Thus when the proper potential is applied between the cathode 33and the anode 40, a large discharge current will flow at a relativelylow voltage. By shutting off the high frequency in the coil 38 when thevoltage between the cathode 33 and the anode 40 reverses, the device canbe made to withstand very high' voltages, and thus rectification of suchhigh voltages may be produced without danger of flashback. Under theseconditions the inability of a self-sustain ing discharge to bemaintained in the side arm 39 assists in the ability of the discharge towithstand such high reverse voltages.

Under proper conditions, the cutting off of the high frequency from thecoil 38 will also prevent the device from conducting current in the for:ward direction; that is, when the cathode 33 is negative and the anode40 is positive. Thus, by impressing a direct current potential betweenthe cathode 33 and the anode 40 and by starting and stopping the highfrequency current in the coil 38, the tube can be made to periodicallyinterrupt the direct current and thus cause the device to act as aninverter.

This invention is not limited to the particular details of constructionor operation as described above, as many equivalents will suggestthemexact pressure which is to be used in each case may vary somewhatwith the type of the tube and the type of gas or vapor. It isaccordingly desired that the appended claims be given a broadinterpretation commensurate with the scope of the invention within theart.

What is claimed is:

1. A gaseous discharge device comprising a sealed envelope containing acathode of the type from which substantial electron emission occursindependently of a discharge, an anode, and an ionizable medium at apressure at which the current flow between said cathode and anode wouldnormally tend to be limited by the space charge created by said electronemission, said pressure being sufficiently high to substantiallyentirely neutralize thespace charge between said cathode and anode upontheoccurrence of an intense ionizing discharge therein, and means forproducing an intense ionizing discharge flowing in a circular paththrough said medium in said envelepe and for introducing the ions sogenerated into the space between said cathode and anode. whereby adischarge at low voltage may take place between said cathode and anode.

an ionizable medium at a pressure at which the current flow between saidcathode and anode would normally tend to be limited by the space chargecreated by said electron emission, said pressurebelng sufficiently highto substantially entirely neutralize the space charge between saidcathode and anode upon the occurrence of an intense ionizing dischargetherein, and means for producing a, periodically varying field in saidmedium in said envelope for producingan elec-..

trodeless discharge therein and for introducing the ions so generatedinto the space between said cathode and anode, whereby a discharge atlow voltage may take place between said cathode and anode.

3. A gaseous discharge device comprising a sealed envelope containing acathode of the type from which substantial electron emission occursindependently of a discharge, an anode, and an ionizable medium at apressure at which the current flow between said cathode and anode wouldnormally tend to be limited bythe space charge created by said electronemission, said pressure being sumciently high to substantially entirelyneutralize the space charge between said cathode and anode upon theoccurrence of an intense ionizing discharge therein, means for producinga periodically varying field in said medium in said envelope forproducing an electrodeless discharge therein and for introducing theions so generated into the space between said cathode and anode, wherebya discharge at low voltage may take place between said cathode andanode, and means for producing av few initial ions and for introducingthem into said high frequency field for starting said electrodelessdischarge.

4. A gaseous discharge device comprising a sealed'envelope containing acathode of the type from which substantial electron emission occursindependently of a discharge, an anode, and an ionizable medium at apressure-at which the current flow between said cathode and anode wouldnormally tend to be limited by the space charge created by said electronemission, said pressure being sufliciently high to substantiallyentirely neutralize the space charge between said cathode and anode uponthe occurrence of an intense ionizing discharge therein, anenlargementformed on said envelope, and means for producing aperiodically varying field in said medium in said enlargement forproducing an electrodeless discharge therein and for introducing theions so generated into the space between said cathode and anode, wherebya discharge at low.

voltage may take place between said cathode and. anode.

5. A gaseous discharge device comprising a sealed envelope containing acathode of the type from which substantial electron emission occursindependently of a discharge, an anode, and an ionizable medium at apressure of the order of .001 mm. or less whereby the current flowbetween said cathode and anode would tend to be limited by space chargein absence of additional means, said pressure being sufficiently high tosubstantially entirely neutralize the space charge between said cathodeand anode upon the occurrence of an intense ionizing discharge therein,and'additional means for producing an intense ionizing discharge throughsaid medium in said envelope and for introducing the ions so generatedinto the space between said cathode and anode, whereby a discharge atlow voltage may take place between said cathode and anode.

i 6. A gaseous discharge device comprising a 1 sealed envelopecontaining a thermionic cathode, an anode, and an ionizable medium at apressure or the order or .001 mm. or less, said pressure beingsufllciently high to substantially entirely neutralize the space chargebetween said cathode and anode upon the occurrence of an intenseionizing discharge therein, and additional means for producing anintense ionizing discharge through said medium in said envelope and forintroducing the ions so generated into the space between said cathodeand anode, whereby a discharge at low voltage may take place betweensaid cathode and anode.

7. A gaseous discharge device comprising a sealed envelope containing acathode of the type from which substantial electron emission occursindependently of a discharge, an anode, and an ionizable medium, meansfor restricting the discharge path intermediate the anode and thecathode to such an extent that cathode and anode would tend to belimited by the space charge created by said electron emission under thenormal pressure conditions in the envelope, said pressure beingsuificiently high to substantially entirely neutralize the space chargebetween said cathode and anode upon the occurrence of an intenseionizing discharge therein, and additional means for producing anintense ionizing discharge through said medium and for introducing saidions into said restricted path, whereby a discharge at low voltage maytake place between said cathode and anode.

8. A gaseous discharge rectifier comprising a sealed envelope containinga cathode, an anode, and an ionizable medium, the pressure of saidmedium being of the order of .001 mm. or less. said pressure beingsuificiently high to substanti'ally entirely neutralize the space chargebetween said cathode and anode upon the occurrence of an intenseionizing discharge therein, and additional means for producing anintense ionizing discharge through said medium in said envelope and forintroducing the ions so generated into the space between said cathodeand anode, whereby a discharge at low voltage may take place betweensaid cathode and anode, said additional means being energized during theperiod when said cathode is positive with respect to said anode anddeenergized during the period when said cathode is negative with respectto said anode, whereby said rectifier is enabled to withstand highreverse voltages.

9. A gaseous discharge device comprising a sealed envelope containing acathode of the type from which substantial electron emission occursindependently of a discharge, an anode, and an ionizable medium, thepressure of said medium being of the order of .001 mm. or less, saidpressure being sufllciently high to substantially entirely neutralizethe space charge between said cathode and anode upon the occurrence ofan intense ionizing discharge therein, and .additional means forproducing an intense ionizing discharge through said medium in saidenvelope and for introducing the ions so generated into the spacebetween said cathode and anode, whereby a discharge at low voltage maytake place between said cathode and anode, said additional means beingdeenergized periodically during the operation of said device to preventconduction of current between cathode and anode during said deenergizedperiod.

10. A gaseous discharge device comprising a sealed envelope containing acathode of the type from which substantial electron emission occursindependently of a discharge, an anode, and an ionizable medium at apressure of the order of .001 mm. or less, said pressure beingsufficiently sealed envelope containing a cathode of the type from whichsubstantial electron emission occurs independently of a discharge, ananode, and an ionizable medium at a pressure at which the current flowbetween said cathode and anode would normally tend to be limited by thespace charge created by said electron emission, said pressure beingsumciently high to substantially entirely neutralize the space chargebetween said cathode and anode upon the occurrence of an intenseionizing discharge therein, and means for producing in said medium anelectrodeless discharge and for introducing the ions so generated intothe space between said cathode and anode, whereby a discharge at lowvoltage may take place between said cathode and anode.

12. The method of operation of a gaseous discharge device comprising asealed envelope containing a cathode of the type from which substantialelectron emission occurs independently of a discharge, an anode, and anionizable medium at a pressure at which current flow between saidcathode and anode would normally tend to be limited by the space chargecreated by said electron emission, said pressure being sufliciently highto substantially entirely neutralize the space charge between saidcathode and anode upon the occurrence of an intense ionizing dischargetherein which comprlses impressing the voltage between said cathode andanode tending to cause a discharge to pass between said electrodes,producing an intense ionizing discharge through said medium byadditional means, and introducing the ions so generated into the spacebetween said cathode and anode to such an extent as to produce a lowvoltage discharge between said cathode and anode.

13. The method of operation of a gaseous discharge device comprising asealed envelope containing a cathode of the type from which substantialelectron emission occurs independently of a discharge, an anode, and anionizable medium at a pressure at which current flow between saidcathode and anode would normally tend to be limited by the space chargecreated by said electron emission, said pressure being sufiiciently highto substantially entirely neutralize the space charge between saidcathode and anode upon the occurrence of an intense ionizing dischargetherein which comprises impressing the voltage between said cathode andanode tending to cause a discharge to pass between said electrodes,producing an intense ionizing electrodeless discharge through saidmedium by additional means, and introducing the ions so generated intothe space between said cathode and anode to such an extent as to producea low voltage discharge between said cathode and anode.

14. The method of operation of a gaseous discharge device comprising asealed envelope containing acathode of'the type from which substantialelectron emission occurs independently, of a discharge, an anode, and aniohizable medium at a pressure at which current flow between saidcathode and anode would normally tend to be limited by the space chargecreated by said electron emission, said pressure being sufiiciently'high to substantially entirely neutralize the space charge between saidcathode and anode upon the occurrence of an intense ionizing dischargetherein which comprises impressing the voltage between said cathode andanode tending to cause a discharge to pass between said electrodes,producing an intense ionizing electrodeless discharge through saidmediumby impressing a periodically-varying magnetic field on said medium, andintroducing the ions so generated into the space between said cathodeand anode to such an extent as to produce a low voltage dischargebetween said cathode and anode.

15. The method of operation of a gaseous discharge device comprising asealed envelope containing a cathode of the type from which substantialelectron emission occurs independently of a discharge, an anode, and anionizable medium at a pressure at which current flow between saidcathode and anode would normally tend to-be limited by the space chargecreated by said electron emission, said pressure being sufliciently highto substantially entirely neutralize the space charge between saidcathode and anode upon the occurrence of an intense ionizing'dischargetherein which comprises impressing the voltage between said cathode andanode tending to cause a discharge to pass between saidelectrodes,producing an intense ionizing discharge through said medium byadditional means, and introducing the ions so generated into the spacebetween said cathode and anode to such an extent as to produce a lowvoltage discharge between said cathode and anode, and interrupting saidintense ionizing discharge produced by said additional means tointerrupt said discharge between said cathode and anode.

16. A gaseous discharge device comprising a sealed envelope containing acathode of the type from which substantial electron emission occursindependently of a discharge, an anode, and an ionizable medium at apressure of the order of .001 mm. or less, whereby the current flowbetween said cathode and anode would normallytend to be limited by spacecharge in absence of additional means, and additional means for pro-,ducing an intense ionizing discharge flowing in a circular path throughsaid medium in said envelope and for introducing the ions so generatedinto the space between said cathode and anode, whereby a discharge atlow voltage may take place between said cathode and anode.

17. A gaseous discharge device comprising a sealed envelope containing acathode of the type from which substantial electron emission occursindependently of a discharge, an anode, and an ionizable medium at apressure of the order of .001 mm, or less, whereby the current flowbetween said cathode and anode would normally tend to be limited byspace charge in absence of additional means, and additional means forproducing a periodically varying field in said medium in said envelopefor producing an electrodeless discharge therein and for introducing theions so generated into the space between said cathode-and anode,whereby, a discharge at low voltage may take place between said cathodeand anode. y

18. A gaseous discharge device comprising a I sealed envelope containinga cathode of the type from which substantial electron emission occursindependently of a discharge, an anode, and an ionizable medium at apressure at .which the current flow between said cathode and anode wouldnormally tend to be limited by the space chargecreated by said electronemission, said pressure being sufliciently high to substantiallyentirely neutralize the space charge between said cathode and anode uponthe occurrence of an intense. ionizing discharge therein, and additionalmeans for producing an intense ionizing discharge through said medium insaid envelope and for introducing the ions so generated into the spacebetween said cathode and anode sufliciently to produce a dischargebetween said cathode and anode at a,voltage drop of the order of theionization voltage of said medium or less.

CHARLES G. SMITH.

